A mechanical refrigerating apparatus includes four major parts, namely, a compressor, an expansion device, a condenser, and an evaporator. The currently available refrigerating systems may be generally divided into three types, namely, direct expansion type, flooded type, and spray type, according to the structure of the evaporator thereof. Wherein, the flooded type and the direct expansion type refrigerating system all belong to a shell-and-tube heat exchanger. In the direct expansion type, refrigerant flows in the tube while the target fluid flows at the shell side. To prevent the liquid refrigerant in the tube from incomplete evaporation and being sucked into the compressor to result in damage of the compressor, the direct expansion type refrigerating system must to increase the superheat at the compressor inlet, which inevitably results in high power consumption of the compressor.
In the flooded type refrigerating system, the target fluid flows in the tube while the refrigerant flows at the shell side. Since the liquid refrigerant is not subject to suction by the compressor at the inlet thereof, it is possible to decrease the superheat of the refrigerant at the compressor inlet and thereby reduce the power consumption of the compressor. However, since the tube of the flooded type evaporator must be immersed in the liquid refrigerant in the shell, an increased quantity of liquid refrigerant is required to immerse the tube located in the shell. As a matter of fact, the quantity of refrigerant required in the flooded type refrigerating system is at least twice as much as that in the direct expansion type refrigerating system to largely increase the equipment cost and environmental burden.
In a spray evaporator, the refrigerant is downward sprayed to form a liquid film on the tube in the shell. As being affected by the force of gravity, pressure and other forces, the liquid film of the sprayed refrigerant moves vertically or in a direction parallel to the tube. When the refrigerant sprayed onto the tube is evaporated, it carries away heat energy of the target fluid inside the heat exchange tube to achieve the purpose of heat exchange. Since the liquid refrigerant flows more quickly on the heat exchange tube surface, it is able to evaporate from the heat exchange tube surface into gaseous refrigerant within a shortened time. In this manner, the heat exchanger may have an enhanced performance, and the cost of the heat exchange tube in the shell could be reduced by at least 25%. Meanwhile, since it is not necessary to immerse the heat exchange tube in a large quantity of liquid refrigerant, the refrigerant charge amount in the mechanical refrigerating apparatus may be reduced by more than 20%. However, many-mechanisms in the spray evaporator, such as the refrigerant distribution control mechanism, have influence on the performance of the spray evaporator. When the mechanism for spraying the refrigerant could not be effectively controlled, the sprayed refrigerant shall become uniformly distributed on the heat exchange tube to result in unnecessary waste of energy of the refrigerating apparatus. U.S. Pat. No. 6,868,695 disclosed a closed-type distributor, where the liquid and gas phase refrigerant therein has to be pressure-driven to spray out. However, the pressure-driven distributor complicates the structure and needs additional devices to pump liquid. Accordingly, a simple and convenient spray type heat-exchanging distributor is still needed